Crash box and method for producing the same

ABSTRACT

A crash box has excellent axial crushing performance and in which, even if the sheet thickness of a tubular body constituting the crash box is smaller than 1.4 mm, good welding can be performed with the tubular body butted against a set plate. The crash box ( 1 ) having a metallic longer-length tubular body and a method for producing the crash box are provided. The tubular body has a basic cross-sectional shape that is a flat polygon surrounded by a plurality of ridges ( 2 - 1  to  2 - 4 ) extending in a longitudinal direction and a plurality of side wall portions ( 4 ), includes one or more groove portions ( 3 - 1  and  3 - 2 ) on side wall portions ( 4 ) on long sides substantially parallel to the major axis direction of the cross section that extend in longitudinal direction, and includes outward flanges ( 5 - 1  to  5 - 4 ) in an end portion in the longitudinal direction.

TECHNICAL FIELD

The present invention relates to a crash box that is to be attached toan automobile body, and to a method for producing the crash box. Inparticular, the present invention relates to, a crash box that is to beattached to, for example, the front portion or the rear portion of anautomobile body and includes a tubular body that buckles and isplastically deformed into a bellows when loaded with impact load in theaxis direction of the tubular body, so as to absorb impact energy, thetubular body being a molded body made of a metal sheet and to a methodfor producing the crash box.

BACKGROUND ART

An impact energy absorbing member that buckles by an impact load in acollision to absorb collision energy is attached to a vehicle. As onesuch impact energy absorbing member, a crash box is known. A crash boxincludes a tubular body that is disposed in the front and rear of avehicle, being oriented in a front-back direction. The crash boxincludes a set plate (an attachment plate) that is welded to thistubular body at one end portion in the longitudinal direction of thetubular body by butt arc welding or the like.

A crash box is required to repeatedly and stably buckle in its axisdirection when loaded with a collision load in the axis direction of thetubular body of the crash box. The present applicants have disclosed in,for example, Patent Document 1, a patented invention relating to a crashbox that includes a tubular body with groove portions. The grooveportions are each provided in such a manner as to project inward from along side of a polygon that forms the cross section of the crash box,and to extend in the axis direction of the crash box. This crash box isensured to, by an impact load loaded in the axis direction, repeatedlybuckle and to be plastically deformed into a bellows so as to absorbimpact energy.

In recent years, in order to reduce the weight of a vehicle, there hasbeen considered the reduction in the sheet thickness of a tubular bodyconstituting a crash box. However, if the sheet thickness of the tubularbody of the crash box disclosed in Patent Document 1 is reduced to about1.2 to 1.4 mm or smaller, the end portion of the tubular body is burnedthrough by heat input in butt arc welding with a set plate, raising therisk of declining the strength of a weld zone.

The present applicant has proposed, in Patent Document 2, a crash boxthat has one end portion in the axis direction of a metallic tubularbody, the one end portion being folded back 180 degrees to be formedinto a folded portion.

LIST OF PRIOR ART DOCUMENTS Patent Document

Patent Document 1: JP3912422B

Patent Document 2: JP2008-261493A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The above problem can be solved with the crash box disclosed in PatentDocument 2 to some extent. However, the crash box has a problem in thatthe existence of the folded portion makes the plastic deformation into abellows hard to occur, which reduces impact energy absorbingperformance, and in that molding the folded portion is difficult if thetubular body is formed of a high-strength steel sheet.

An objective of the present invention is to provide a lightweight crashbox and a method for producing the crash box, the crash box including atubular body that can be well welded, with the tubular body buttedagainst a set plate, even if the sheet thickness of the tubular bodyconstituting the crash box is smaller than 1.4 mm.

Means for Solving the Problems

The present invention will be described as follows.

(1) A crash box comprising a longer-length metallic tubular body,

the tubular body having a basic cross-sectional shape that is a polygonsurrounded by a plurality of ridges extending in one direction and aplurality of side wall portions, the tubular body including one or moregroove portions in side wall portions on long sides that aresubstantially parallel to the major axis direction of the cross section,the groove portions extending in the one direction, and the tubular bodyincluding outward flanges in an end portion in the one direction.

In other words, in the crash box that includes a longer-length tubularbody made of a steel sheet, the tubular body having a basiccross-sectional shape that is a polygon surrounded by a plurality ofridges extending in one direction and a plurality of side wall portions,the tubular body including one or more groove portions in side wallportions on long sides substantially parallel to the major axisdirection of the cross section, the groove portions extending in the onedirection, characterized in that the tubular body includes outwardflanges in an end portion in the one direction.

In the present invention, if the polygon is a rhombus, the long side inthe present invention refers to each side of the rhombus.

(2) The crash box according to the section 1, wherein the polygon is aflat polygon.(3) The crash box according to the section 1 or the section 2, whereinthe outward flanges are provided in all the ridges excluding at leastregions of the end portion corresponding to a groove portion.(4) The crash box according to any one of the section 1 to the section3, wherein the outward flanges are molded integrally with the tubularbody.(5) The crash box according to any one of the section 1 to the section4, wherein the tubular body is a press molded body of the metal sheet.(6) The crash box according to any one of the section 1 to the section5, wherein the metal sheet has a sheet thickness of 1.2 mm or smaller.(7) The crash box according to any one of the section 1 to the section5, wherein the metal sheet has a sheet thickness of 1.0 mm or smaller.(8) The crash box according to any one of the section 1 to the section7, wherein the metal sheet is a steel sheet having a tensile strength of440 MPa or higher.(9) The crash box according to any one of the section 1 to the section7, wherein the metal sheet is a steel sheet having a tensile strength of590 MPa or higher.(10) The crash box according to any one of the section 1 to the section9, wherein the polygon is a substantial quadrilateral.(11) The crash box according to any one of the section 1 to the section10, further comprising a set plate that is welded with the outwardflanges interposed therebetween.(12) The crash box according to the section 11, wherein the set plateincludes a locking section that is provided projecting from a surface ofthe plate and is butted against an inner surface of an end portion in alongitudinal direction of the tubular body.(13) The crash box according to claim 12, wherein the locking sectionincludes a curved portion (rise-up curvature portion) that is buttedagainst a curved portion formed in an end portion in one direction ofthe tubular body so as to support the curved portion.(14) A method for producing the crash box according to any one of thesection 1 to the section 10, the method comprising following First Stepand Second Step;

First Step: a step of, using a pressing device including: a punch thatincludes a groove portion that extends in one direction and a side wallprovided in an end portion in the one direction; a die that is disposedfacing the punch; and a pad that includes a protrusion extending in theone direction, to depress a developed blank of the tubular body into thegroove portion of the punch by a protrusion of the pad and bend thedeveloped blank using the die and the punch, so as to produce two pressmolded bodies with an open cross-section, the press molded bodies eachhaving a basic cross-sectional shape that is a polygon surrounded by aplurality of ridges extending in the one direction and a plurality ofside wall portions, the press molded bodies each including one or moregroove portions in side wall portions on long sides substantiallyparallel a major axis direction of the cross section, the grooveportions extending in the one direction, and the press molded bodieseach including outward flanges in an end portion in the one direction,the outward flanges being continuous in a part of region along across-section circumferential direction; and

Second Step: a step of overlapping and welding the two press moldedbodies produced through the first step, at plane portions that are eachformed at both ends in a cross-section circumferential direction of eachof the two press molded bodies, so as to produce the tubular body.

(15) The method for producing a crash box according to the section 14,wherein the pad includes restraining portions that restrain portions inthe developed blank to be molded into ridges in a vicinity of outwardflanges, the portions in the developed blank to be molded into the ridgein the vicinity of the outward flanges are retained by the restrainingportions.(16) A method of producing the crash box according to any one of thesection 11 to the section 13, the method comprising following FirstStep, Second Step, and Third Step;

First Step: a step of, using a pressing device including: a punch thatincludes a groove portion that extends in one direction and a side wallprovided in an end portion in the one direction; a die that is disposedfacing the punch; and a pad that includes a protrusion extending in theone direction, to depress a developed blank of the tubular body into thegroove portion of the punch by a protrusion of the pad and bend thedeveloped blank using the dies and the punch, so as to produce two pressmolded bodies with an open cross-section, the press molded bodies eachhaving a basic cross-sectional shape that is a polygon surrounded by aplurality of ridges extending in the one direction and a plurality ofside wall portions, the press molded bodies each including one or moregroove portions in side wall portions on long sides substantiallyparallel a major axis direction of the cross section, the grooveportions extending in the one direction, and the press molded bodieseach including outward flanges in an end portion in the one direction,the outward flanges being continuous in a part of region along across-section circumferential direction; and

Second Step: a step of overlapping and welding the two press moldedbodies produced through the first step, at plane portions that are eachformed at both ends in a cross-section circumferential direction of eachof the two press molded bodies, so as to produce the tubular body.

Third Step: a step of overlapping the tubular body obtained through thesecond step and the set plate with the outward flanges interposedtherebetween, and attaching the tubular body to the set plate by spotwelding, fillet arc welding, or laser welding.

(17) The method for producing a crash box according to claim 16, whereinthe set plate includes a locking section that is provided projectingfrom a surface of the plate and is butted against an inner surface of anend portion in a longitudinal direction of the tubular body.

Advantageous Effects of the Invention

According to the present invention, it is possible to perform spotwelding, fillet arc welding, or laser welding with outward flangesformed on a tubular body and a set plate made to overlap with eachother. For this reason, even if the sheet thickness of the tubular bodyis less than 1.4 to 1.2 mm, the occurrence of poor welding such asburn-through, which is a problem with the prior art, is prevented,increasing strength in a weld zone. This allows for providing alightweight crash box that includes a tubular body having a sheetthickness of less than 1.4 to 1.2 mm.

In addition, in a crash box including curved portions (rise-up curvatureportions) and outward flanges in an end portion in a longitudinaldirection, in the case where the sheet thickness of a tubular body is,in particular, smaller than 1.2 mm, an impact load causes the endportion in the longitudinal direction of the tubular body to collapseinside the cross section, generating deformation that hinders stablerepetitive buckling. This phenomenon occurs conspicuously in particularwhen the impact load acts in a direction oblique to the axis directionof the tubular body.

The present invention uses a set plate including locking sections thatare provided projecting from a surface of the plate and are buttedagainst the inner surface of the tubular body to retain an end portionin the longitudinal direction of the tubular body. Accordingly, it ispossible to suppress the above collapse, increasing the impact energyabsorbing performance of a crash box that includes a tubular body havinga small sheet thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative diagram illustrating a tubular body thatconstitutes a crash box of the present embodiment, where FIG. 1A is aperspective view illustrating the entirety thereof, FIG. 1B is a frontview, FIG. 1C is a side view, and FIG. 1D to F are illustrative diagramsillustrating examples of the positions of outward flanges.

FIG. 2 is an illustrative diagram schematically illustrating the statewhere the tubular body and a set plate of the crash box are attached toeach other.

FIGS. 3A-C are illustrative diagrams schematically illustrating lockingsections provided in the set plate, with FIG. 3A showing a plan view ofthe set plate, FIG. 3B showing a cross sectional view taken along theline I-1, and FIG. 3C showing a diagram of the set plate and tubularbody combined.

FIG. 4 is a schematic diagram illustrating an example of theconfiguration of a pressing device for producing a press molded body.

FIG. 5 is a schematic diagram illustrating the other example of theconfiguration of the pressing device for producing the tubular body ofthe embodiment.

FIG. 6 is an illustrative diagram schematically illustrating a methodfor producing a crash box according to the present invention, where FIG.6A illustrates First Step, FIG. 6B illustrates Second Step, and FIG. 6Cillustrates Third Step.

FIGS. 7A and 7B are illustrative diagrams schematically illustrating theshapes of developed blanks in examples.

FIGS. 8A and 8B are illustrative diagrams schematically illustrating theshapes press molded bodies in the examples.

MODE FOR CARRYING OUT THE INVENTION

The present invention will be described with reference to theaccompanying drawings.

1. Crash box 0

FIG. 1 is an illustrative diagram illustrating a tubular body 1 thatconstitutes a crash box 0 according to the present invention, where FIG.1A is a perspective view illustrating the entirety thereof, FIG. 18B isa front view of the tubular body 1, FIG. 1C is a side view of thetubular body 1, and FIGS. 1D to F are cross sectional views ofmodifications 1-1 to 1-3 of the tubular body 1.

The crash box 0 includes a metallic tubular body 1. The tubular body 1buckles into a bellows upon receiving an impact load that is applied inthe axis direction of the tubular body 1, so as to absorb collisionenergy.

As illustrated in FIGS. 1A and 1B, the tubular body 1 has a basic crosssection that is a flat substantial quadrilateral. The tubular body 1includes one or more groove portions 3-1 and 3-2 each of which extendsin the longitudinal direction of the tubular body 1. The groove portions3-1 and 3-2 are provided in positions excluding ridges 2-1 to 2-4 thatconstitute the basic cross section. The groove portions 3-1 and 3-2 areprovided in side wall portions 4 on long-side face sides that areparallel to the major axis direction of the cross section. The grooveportions 3-1 and 3-2 are groove portions each projecting toward theinside of the cross section.

In this description, the tubular body 1 is used that has a crosssectional shape being a substantial quadrilateral. However, the presentinvention is not limited to this cross-sectional shape. The tubular body1 in the present invention may have a cross sectional shape of, forexample, a flat substantial polygon such as a hexagon and an octagon.Preferably, the basic cross section is a flat substantial quadrilateral,and one or more groove portions 3-1 and 3-2 are formed in two side wallportions 4 and 4 on long-side face sides.

As illustrated in FIGS. 1A and 1B, the tubular body 1 is formed by afirst press molded body 10-1 and a second press molded body 10-2 incombination, which will be described later. Each of the first pressmolded body 10-1 and the second press molded body 10-2 is a press moldedbodies made of a metal sheet.

In an end portion of the tubular body 1 in its longitudinal direction,outward flanges 5-1 to 5-4 are provided in the region of the side wallportion 4 excluding the groove portions 3-1 and 3-2. The outward flanges5-1 to 5-4 are molded integrally with the tubular body 1.

The outward flanges 5-1 to 5-4 includes flat portions along thecircumferential direction of the cross-section, the flat portions eachhaving a width of 2 mm or more. A width B1 of the outward flanges 5-1 to5-4 along the ridges 2-1 to 2-4 is 2 mm or more. A width B2 of theoutward flanges 5-1 to 5-4 along the region other than the ridges 2-1 to2-4 is 10 mm or more. Now, the width of the flange means a length in adirection perpendicular to the cross-section circumferential directionof the outward flange region (the length of only the flat portion, notincluding a curved portion).

This description will be made about the case where spot welding with theset plate is not performed on the outward flanges 5-1 to 5-4 along theridges 2-1 to 2-4, but on outward flanges 5-1 to 5-4 along the regionother than the ridges 2-1 to 2-4. The present invention is not limitedto this case. As illustrated in FIG. 1D, the outward flanges 5-1 to 5-4may be provided at least in the range along the ridges 2-1 to 2-4, andas illustrated in FIG. 1E, it is preferable that, in addition to theridges 2-1 to 2-4, outward flanges 5-5 and 5-6 are provided onshort-side side wall portions 6-1 and 6-2, such that all portions otherthan the groove portions are provided with the outward flanges. Asillustrated in FIG. 1F, it is more preferable that an outward flange 5-7is provided on the entire circumference of the cross-section.

The width of the outward flanges 5-1 to 5-4 is 2 mm or more in portionswhere laser welding or fillet arc welding is to be performed, and 10 mmor more in portions where spot welding will be performed.

The cross-sectional shape of the groove portions 3-1 and 3-2 each havesubstantial trapezoid or triangular shape, the groove depth of which is10 to 35 mm. If the width of the bottom of the groove portions 3-1 and3-2 is insufficient, or if the depth of the groove bottoms 3-1 and 3-2is insufficient, the buckling deformation of the tubular body 1 becomesunstable, and it is thus difficult to obtain sufficiently theadvantageous effect of improving an impact energy absorbing performancethat is brought by the provision of the groove portions 3-1 and 3-2.

The length of the tubular body 1 in its axis direction is 80 to 300 mm,from the practical viewpoint.

The sheet thickness of the tubular body 1 is assumed to be smaller than1.4 mm, but is not limited to this configuration, and can be 1.4 mm orlarger. Note that the sheet thickness is preferably smaller than 1.4 mm,more preferably 1.2 mm or smaller, and most preferably 1.0 mm orsmaller. The lower limit value of the sheet thickness of the tubularbody 1 is preferably 0.5 mm or higher, from the viewpoint of ensuring adesired energy absorption. This allows achieving the reduction of thecrash box 0 in weight.

The material of the tubular body 1 is assumed to be made of a metal, andpreferably made of a steel sheet, more preferably made of a high-tensilesteel sheet having a tensile strength of 440 MPa or higher, and stillmore preferably made of a high-tensile steel sheet having a tensilestrength of 590 MPa or higher.

FIG. 2 is an illustrative diagram illustrating the state where thetubular body 1 and a set plate 7, which constitute the crash box 0, areattached to each other.

As illustrated in FIG. 2, the crash box 0 includes the tubular body 1,which is described above, and the set plate 7. The set plate 7 isattached to the tubular body 1 with the outward flanges 5-1 to 5-4provided in one end portion of the tubular body 1 interposedtherebetween, by welding. One such welding is laser welding, fillet arcwelding, spot welding, or the like.

FIG. 3 is an illustrative diagram schematically illustrating lockingsections 8-1 to 8-4 that are provided in the set plate 7, where FIG. 3Ais a plan view of the set plate 7, FIG. 3B is a cross sectional view ofthe set plate 7 taken along the line I-I, and FIG. 3C is an illustrativediagram schematically illustrating the state where the tubular body 1are the set plate 7 are combined with each other.

As illustrated in FIG. 3, the set plate 7 includes the locking sections8-1 to 8-4. The locking sections 8-1 to 8-4 are provided projecting froma surface of the plate 7. The locking sections 8-1 to 8-4 are buttedagainst the inner surface of the tubular body 1 to retain one endportion in the longitudinal direction of the tubular body 1. That is,the locking sections 8-1 to 8-4 support the portions, along the ridges2-1 to 2-4, of the curved portions (rise-up curvature portions) of theoutward flanges 5-1 to 5-4 in one end portion in the longitudinaldirection of the tubular body 1, from the inside of the main body 1. Thelocking sections 8-1 to 8-4 preferably retain all the portions of thecurved portions (rise-up curvature portions) of the outward flanges 5-1to 5-4 excluding the groove bottom portion, from the inside of thetubular body 1.

As seen above, the locking sections 8-1 to 8-4 preferably have curvedportions 8 a that are configured to be butted against the curvedportions (rise-up curvature portions) of the outward flanges 5-1 to 5-4so as to support the curved portions.

Note that it is preferable that the set plate 7 is formed integrally. Inthis case, instead of forming the four locking sections 8-1 to 8-4individually, but for example, the locking sections 8-1 and 8-4 may beintegrally and consecutively formed while the locking sections 8-2 and8-3 may be integrally and consecutively formed. In addition, lockingsections 8-5 and 8-6 may be further provided together with the lockingsections 8-1 and, 8-4. The locking sections 8-5 and 8-6 retain portionscorresponding to the groove portions 3-1 and 3-2 from the inside of thetubular body 1.

The locking sections 8-1 to 8-4 may exist in the curved portions(rise-up curvature portions) of the flanges of the tubular body 1, forexample, in the portions corresponding to RI to 10 mm. The lockingsections 8-1 to 8-4 each preferably have a height that is about one toten times the sheet thickness of a metal sheet forming the flange. Theset plate 7 is manufactured by pressing, for example, a steel sheethaving a tensile strength of 270 to 980 MPa-class.

The crash box 0 according to the present invention is configured asdescribed above.

2. Method for Manufacturing Crash Box 0

FIG. 6 is an illustrative diagram schematically illustrating a methodfor producing the crash box 0 according to the present invention, whereFIG. 6A illustrates a first step, FIG. 6B illustrates a second step, andFIG. 6C illustrates a third step.

The tubular body 1 that constitutes the crash box 0 through:

First Step: producing two press molded bodies 10 each having an opencross-section from developed blanks, which will be described later (FIG.6A); andSecond Step: producing the tubular body 1 from the two press moldedbodies 10 and 10 (FIG. 6B).

Furthermore, as illustrated in FIG. 6C, the crash box 0 including thetubular body 1 and the set plate 7 is produced through a third step ofattaching the set plate 7, by spot welding or the like, to the tubularbody 1 that is produced through the second step. Note that the two pressmolded bodies 10 and 10 both have an open cross-sectional shape that isobtained by dividing the tubular body 1 into substantially two equalportions by a plane including the central axis of the tubular body 1.

[First Step]

FIG. 4 is a schematic diagram illustrating an example of theconfiguration of a pressing device 11 for producing the press moldedbody 10.

In the first step, the pressing device 11 is used as illustrated in FIG.4. The pressing device 11 includes a punch 12, a die 13, and a pad 14.The punch 12 includes a groove portion 12 a that extends in onedirection (the longitudinal direction), and a side wall 12 b that isprovided in an end portion in the longitudinal direction. The die 13 isdisposed facing the punch 12. The pad 14 includes a protrusion 14 a thatextends in the longitudinal direction and is disposed facing the punch12.

By press molding the developed blanks 15 using the pressing device 11,two press molded bodies 10, namely, a first press molded body 10-1 and asecond press molded body 10-2 are produced. The two press molded bodies10 have groove portions 3-1 and 3-2 that run in one direction andincludes outward flanges 5-1 to 5-4 that are formed in one end portionof a longitudinal direction.

In the press molding in the first step, the developed blank 15 isdepressed into the groove portion 12 a of the punch 12 by the protrusion14 a provided in the pad 14, and the developed blank 15 is bent by thedie 13 and the punch 12. This yields a metal sheet provided with agroove portion 3-1 that runs in the longitudinal direction and outwardflanges 5-1 and 5-2 that are formed in an end portion in thelongitudinal direction, in at least regions along a circumferentialdirection in the cross-section excluding the groove portion 3-1.Hereafter, the pad 14 will be also referred to as a normal pad.

Note that the developed blank 15 refers to a blank having an externalshape obtained by developing the press molded body 10 to a flat shape.

The above description of the first step is made about a method of pressmolding using the pressing device 11, but the first step is not limitedto this molding method.

As the other molding method, for example, a pressing device 16illustrated in FIG. 5 can be used.

FIG. 5 is a schematic diagram illustrating a configuration example ofthe pressing device 16 that is the other pressing device for producingthe press molded body 10.

The pressing device 16 includes a punch 12 and a die 13 and furtherincludes a pad 17 (hereafter, also referred to as a ridge pad). Thepunch 12 includes a groove portion 12 a that extends in one direction,and a side wall 12 b that is provided in an end portion in thelongitudinal direction. The die 13 is disposed facing the punch 12. Thepad 17 includes a protrusion 17 a that is disposed facing the punch 12and runs in one direction, and restraining portions 17 b that restrainthe vicinity of portions in the developed blank 15 that are to be moldedinto ridges 2-1 and 2-2 in the vicinity of the outward flanges 5-1 and5-2.

In press molding, the restraining portions 17 b restrain the portions inthe developed blank 15 that are to be molded into the ridges 2-1 and 2-2in the vicinity of the outward flanges 5-1 and 5-2. In addition, theprotrusion 17 a of the ridge pad 17 depresses the developed blank 15 tothe groove portion 12 a of the punch 12. Furthermore, the die 13 and thepunch 12 bend the developed blank 15. This suppresses poor molding thatoccurs in the outward flanges 5-1 and 5-2 along the ridges 2-1 and 2-2in press molding.

This produces the press molded body 10, the open cross-section of whichhas the groove portion 3-1 extending in the longitudinal direction andthe outward flanges 5-1 and 5-2, in an end portion in the longitudinaldirection, the outward flanges 5-1 and 5-2 being continuous in theentire or a part of the region along the cross-section circumferentialdirection.

If portions or the like right under the ridge pad 17 corresponding tothe ridges 2-1 and 2-2 are not completely molded in the molding processusing the ridge pad 17, the portions may be molded by following pressworking that includes bending (restrike), which is performed in typicalpress molding.

[Second Step]

In the second step, the first press molded body 10-1 and the secondpress molded body 10-2 are made to overlap each other at plane portionsthat are formed at both ends of their cross-section circumferentialdirection, and the overlapping portions are attached to each other byappropriate welding means such as laser welding and spot welding, so asto produce the tubular body 1.

[Third Step]

In the third step, the tubular body 1 obtained in the second step iswelded to the set plate 7 with the outward flanges 5-1 to 5-4 interposedtherebetween, by welding means such as laser welding, spot welding, andfillet arc welding. As the set plate 7, it is preferable to use a setplate provided with the locking sections 8-1 to 8-4.

In the above description, the employed form is a form that includes thecontinuous outward flanges 5-1 to 5-4 in the region excluding the grooveportion, but is not limited to this form, and may be a form in which theoutward flanges 5-1 to 5-4 formed in the above region have notches inportions of the flanges other than those corresponding to the ridges 2-1to 2-4 excluding the groove portions.

The width or shape of the outward flanges 5-1 to 5-4 can be modified asappropriate by adjusting the shape of the developed blank 15.

EXAMPLE

Deformation behavior in the press molding of developed blanks into thepress molded bodies 10-1 and 10-2 (the first and the second press moldedbodies) using the pressing device 11 including the normal pad 14illustrated in FIG. 4 or the pressing device 16 including the ridge pad17 illustrated in FIG. 5, was analyzed by Finite Element Method)(Analysis 1).

FIG. 7 is an illustrative diagram schematically illustrating shapes ofdeveloped blanks 15-1 and 15-2 in the example.

As the developed blanks, as illustrated in FIGS. 7A and 7B, the blanks15-1 and 15-2 of two types were used that were adjusted such that theoutward flanges 5-1 to 5-4 to be formed in an end portion of the tubularbody 1 were formed in the entire region in the cross-sectioncircumferential direction excluding parts of region along the grooveportions 3-1 and 3-2. The developed blank 15-1 was formed such that thewidth of the outward flanges 5-1 to 5-4 was substantially uniform and 15mm. The developed blank 15-2 was formed such that the width of theoutward flanges 5-1 to 5-4 along the ridges 2-1 to 2-4 was 2 mm and thewidth of the other portions was 15 mm.

FIG. 8 is an illustrative diagram schematically illustrating the shapesof a press molded body 10-pattern A and a press molded body 10-pattern Bin the examples, where FIG. 8A illustrates the case of using thedeveloped blank 15-1, and FIG. 8B illustrates the case of using thedeveloped blank 15-2.

Next, molded bodies were made to overlap each other at plane portions,the molded bodies being each of two first press molded bodies 10-patternA and two second press molded body 10-pattern B to which flanges areadded in groove bottom portions, the plane portions each being formed atboth ends in a cross-section circumferential direction of each of themolded bodies, and the overlapping portions are subjected to spotwelding to produce a tubular body 1 that includes outward flanges 5-1 to5-4.

Next, a crash box 0 was assembled, which includes the tubular body 1 anda set plate 7 that is subjected to spot welding with the outward flanges5-1 to 5-4 provided in an end portion of the tubular body 1 interposedtherebetween, and buckling behavior at the time of applying impact loadto one end of the tubular body 1 constituting the crash box 0 wasanalyzed by Finite Element Method (Analysis 2).

Note that there were two loading directions of the impact load, adirection parallel to the longitudinal direction of the tubular body 1and a direction that inclines 5 degrees with respect to the longitudinaldirection.

The tubular body 1 had a length of 120 mm and a cross-sectionaldimension of 64 mm×93 mm.

The material of the blanks 15-1 and 15-2 were JSC440W (The Japan Ironand Steel Federation Standard (JFS Standard)), which is a 440 MPa-classcold-rolled steel sheet, and JSC590R (JFS Standard), which is a 590MPa-class cold-rolled steel sheet, and there were two levels of sheetthickness, 1.0 mm and 1.2 mm.

In addition, the influence of the presence/absence of the lockingsections 8-1 to 8-4 in the set plate 7 was also examined. The lockingsections 8-1 to 8-4 each have shapes corresponding to the shape of acurved portion (rise-up curvature portion), having an inner R of 2 to 4mm, and the height of the locking sections 8-1 to 8-4 is about 3 to 7mm, which is somewhat higher than the value of the inner R.

As a conventional example, a similar analysis was conducted on a crashbox produced by performing butt arc welding on a known tubular body thatwas butted against a set plate, the known tubular body having thecross-sectional shape of the tubular body 1 described above and notincluding outward flanges 5-1 to 5-4. The material of the blank wasJSC440W, and there were two levels of sheet thickness, 1.0 mm and 1.2mm.

Table 1 shows the results of Analysis 1. As illustrated in Table 1, boththe developed blanks 15-1 and 15-2 can yield a press molded body thatincludes groove portions 3-1 and 3-2 that extends in their longitudinaldirection, and outward flanges 5-1 and 5-2 or outward flanges 5-3 and5-4 in an end portion of the longitudinal direction, but with thedeveloped blank 15-1, as compared with the developed blank 15-2, thereis a large increase in sheet thickness at the roots of the outwardflanges 5-1 and 5-2 or the outward flanges 5-3 and 5-4 along ridges 2-1and 2-2 or ridges 2-3 and 2-4, in press molding, and there is a largedecrease in sheet thickness at the edges of the outward flanges 5-1 and5-2 or the outward flanges 5-3 and 5-4 along the ridges 2-1 and 2-2 orthe ridges 2-3 and 2-4.

Alternatively, in the case of using the ridge pad 17, an increase insheet thickness at the roots and a decrease in sheet thickness at theedges are small, which is good as compared with the case of using thenormal pad 14. Therefore, from the viewpoint of avoiding the occurrencewrinkles with the increase in sheet thickness and the occurrence offlange cracks with the decrease in sheet thickness, it is desirable toperform press molding using the ridge pad 17. In addition, it isdesirable, as the developed blank 15-2, to make the width of the outwardflanges 5-1 and 5-2 or the outward flanges 5-3 and 5-4 along thevicinity of the ridges 2-1 and 2-2 or the ridges 2-3 and 2-4 smallerthan the width of the outward flanges 5-1 and 5-2 or the outward flanges5-3 and 5-4 in the other region.

TABLE 1 Sheet thickness fluctuations in the vicinity of ridges SheetDeveloped Decreasing rate in Increase rate in Number Material thicknessblank Pad sheet thickness *1 sheet thickness *2 1 JSC590R 1.0 mm ANormal pad 22% 35% 2 JSC590R 1.0 mm B Normal pad 15%  3% 3 JSC590R 1.0mm A Ridge pad 17% 19% *1: Outer end portions of outward flang *2: Rootportions of outward flanges

Table 2 shows principal conditions of Analysis 2, and Table 3 and Table4 show the analysis results and weldabilities in comparison.

TABLE 2 Material and Presence/absence sheet Shape and width of ofprojecting in set Example thickness outward flanges plate Collision faceof impactor Inventive JSC 590R FIG. 8(a) Present Perpendicular tolongitudinal example 1 1.0 mm About 15 mm over entire direction oftubular body perimeter Inventive JSC 590R FIG. 8(b) PresentPerpendicular to longitudinal example 2 1.0 mm 2 mm in ridges, 15 mm indirection of tubular body other portions Inventive JSC 590R FIG. 8(b)Absent Perpendicular to longitudinal example 3 1.0 mm 2 mm in ridges, 15mm in direction of tubular body other portions Inventive JSC 440W FIG.8(b) Present Perpendicular to longitudinal example 4 1.0 mm 2 mm inridges, 15 mm in direction of tubular body other portions Inventive JSC440W FIG. 8(b) Present Inclined 5 degrees, with example 5 1.0 mm 2 mm inridges, 15 mm in respect to plane other portions perpendicular tolongitudinal direction of tubular body, about an axis of rotation thatis an axis perpendicular to top surface Conventional JSC 440W AbsentAbsent Perpendicular to longitudinal example 1 1.0 mm direction oftubular body Inventive JSC 590R FIG. 8(a) Present Perpendicular tolongitudinal example 6 1.2 mm About 15 mm over entire direction oftubular body perimeter Inventive JSC 590R FIG. 8(b) PresentPerpendicular to longitudinal example 7 1.2 mm 2 mm in ridges, 15 mm indirection of tubular body other portions Inventive JSC 590R FIG. 8(b)Absent Perpendicular to longitudinal example 8 1.2 mm 2 mm in ridges, 15mm in direction of tubular body other portions Inventive JSC 440W FIG.8(b) Present Perpendicular to longitudinal example 9 1.2 mm 2 mm inridges, 15 mm in direction of tubular body other portions Inventive JSC440W FIG. 8(b) Present Inclined 5 degrees, with example 10 1.2 mm 2 mmin ridges, 15 mm in respect to plane other portions perpendicular tolongitudinal direction of tubular body, about an axis of rotation thatis an axis perpendicular to top surface Conventional JSC 440W AbsentAbsent Perpendicular to longitudinal example 2 1.2 mm direction oftubular body

TABLE 3 Buckling Absorbed Absorbed Examples Weldability behavior energy*1 energy *2 Inventive example 1 Good Very stable 98% 118% Inventiveexample 2 Good Very stable 94% 112% Inventive example 3 Good Somewhat85% 102% unstable Inventive example 4 Good Very stable 73%  88%Inventive example 5 Good Stable 66%  80% Conventional Poor — — — example1 *1: Ratio of absorbed energy at a stroke of 90 mm, it is 100% with aconventional example 2 (to be described) *2: Ratio of absorbed energy ofper unit weight at a stroke of 90 mm, it is 100% with the conventionalexample 2 (to be described)

TABLE 4 Absorbed Absorbed Examples Weldability Buckling behavior energy*1 energy *2 Inventive Good Very stable 127% 127% example 6 InventiveGood Very stable 128% 128% example 7 Inventive Good Somewhat 127% 127%example 8 unstable Inventive Good Very stable 104% 104% example 9Inventive Good Stable 92% 92% example 10 Conventional Somewhat Verystable 100% 100% example 2 poor*3 *1: Ratio of absorbed energy at astroke of 90 mm, it is 100% with the conventional example 2 *2: Ratio ofabsorbed energy of per unit weight at a stroke of 90 mm, it is 100% withthe conventional example 2 *3: “Somewhat poor” means that “it canproduce a good product, but it is inferior to Inventive Examples in thestability of welding in mass production”

As shown in Tables 2 and 3, the conventional Example 1 has a sheetthickness of 1.0 mm, which causes burn-through to easily occur in buttarc welding, making it difficult to produce the crash box.

In contrast to this, with the inventive examples 1 to 5, it is possibleto perform spot welding on the tubular body 1 to the set plate 7 withthe outward flanges 5-1 and 5-2 or the outward flanges 5-3 and 5-4interposed therebetween, which is available for an impact energyabsorbing structure for an automobile body. In particular, it was foundabout the inventive examples 1, 2, and 4, in which the locking sections8-1 to 8-4 provided in the set plate 7 support the ridges 2-1 to 2-4 ofthe tubular body 1 from the inside thereof, that the sheet thicknessthereof is 1.0 mm, but a collapse of root R portions toward the insideof the cross section in an end portion in the longitudinal direction issuppressed, resulting in a very stable buckling behavior, as with theconventional example 2 the sheet thickness of which is 1.2 mm.

In addition, as illustrated by the inventive example 5, it was foundthat the crash box exhibits stable buckling behavior even when a face tocollide (impactor) inclines with respect to a face perpendicular to thelongitudinal direction axis of the tubular body 1. Note that, in theinventive example 3, a phenomenon was recognized that the root Rportions of the outward flanges 5-1 and 5-2 or the outward flanges 5-3and 5-4 slightly collapses toward the inside of the cross section, inthe initial stage of impactor stroke.

According to the present invention, it is possible to attach, by spotwelding or the like, the tubular body 1 to the set plate 7 with theoutward flanges 5-1 and 5-2 or the outward flanges 5-3 and 5-4interposed therebetween, enabling the prevention of poor welding such asburn-through in conventional butt arc welding even for a tubular body 1having a small sheet thickness, and thus it is possible to produce alightweight crash box having an excellent impact energy absorbingperformance.

In addition, it is understood by comparing between the inventiveexamples 9 and 10 with the conventional example 2 in Tables 2 and 4that, according to the present invention, it is possible to ensure agood weldability while keeping substantially the same energy absorptionand stable buckling behavior as those of the conventional example.

REFERENCE SIGNS LIST

-   0 Crash box-   1 Tubular body-   2-1 to 2-4 Ridge-   3-1, 3-2 Groove portion-   5-1 to 5-4 Outward flange

1-17. (canceled)
 18. A method of producing crash box comprising alonger-length metallic tubular body and a set plate including lockingsections, the locking sections are individually formed as a part of theset plate, the tubular body having a basic cross-sectional shape that isa polygon surrounded by a plurality of ridges extending in a firstdirection and a plurality of side wall portions, the tubular bodyincluding one or more groove portions in side wall portions on longsides that are substantially parallel to a major axis direction of thecross section, the groove portions extending in the first direction, andthe tubular body including a curved portion molded integrally with thetubular body and outward flanges continuing to the curved portion at anend portion of the tubular body in the first direction, the set platebeing welded to an end of the tubular body having the outward flanges,and the locking sections section being integral with the set plate andprojecting upwardly from a surface of a portion of the set platepositioned within the tubular body, wherein the locking sections sectionof the set plate are is butted against the curved portion of the tubularbody, wherein the method comprising following First Step, Second Step,and Third Step; First Step: a step of, using a pressing deviceincluding: a punch that includes a groove portion that extends in asecond direction and a side wall provided in an end portion in thesecond direction; a die that is disposed facing the punch; and a padthat includes a protrusion extending in the second direction, to depressa developed blank of the tubular body into the groove portion of thepunch by a protrusion of the pad and bend the developed blank using thedie and the punch, so as to produce two press molded bodies with an opencross-section, the press molded bodies each having a basiccross-sectional shape that is a polygon surrounded by a plurality ofridges extending in the second direction and a plurality of side wallportions, the press molded bodies each including one or more grooveportions in side wall portions on long sides substantially parallel amajor axis direction of the cross section, the groove portions extendingin the second direction, and the press molded bodies each includingoutward flanges in an end portion in the second direction, the outwardflanges being continuous in a part of region along a cross-sectioncircumferential direction; and Second Step: a step of overlapping andwelding the two press molded bodies produced through the first step, atplane portions that are each formed at both ends in a cross-sectioncircumferential direction of each of the two press molded bodies, so asto produce the tubular body. Third Step: a step of overlapping thetubular body obtained through the second step and the set plate with theoutward flanges interposed therebetween, and attaching the tubular bodyto the set plate by spot welding, fillet arc welding, or laser welding.19. The method for producing a crash box according to claim 18, whereinthe polygon is a flat polygon.
 20. The method for producing a crash boxaccording to claim 18, wherein the outward flanges are provided in allthe ridges excluding at least regions of the end portion correspondingto a groove portion.
 21. The method for producing a crash box accordingto claim 18, wherein the outward flanges are molded integrally with thetubular body.
 22. The method for producing a crash box according toclaim 18, wherein the tubular body is a press molded body of the metalsheet.
 23. The method for producing a crash box according to claim 18,wherein the metal sheet has a sheet thickness of 1.2 mm or smaller. 24.The method for producing a crash box according to claim 18, wherein themetal sheet has a sheet thickness of 1.0 mm or smaller.
 25. The methodfor producing a crash box according to claim 18, wherein the metal sheetis a steel sheet having a tensile strength of 440 MPa or higher.
 26. Themethod for producing a crash box according to claim 18, wherein themetal sheet is a steel sheet having a tensile strength of 590 MPa orhigher.
 27. The method for producing a crash box according to claim 18,wherein the polygon is a substantial quadrilateral.
 28. The method forproducing a crash box according to claim 18, wherein the pad includesrestraining portions that restrain portions in the developed blank to bemolded into ridges in a vicinity of outward flanges, the portions in thedeveloped blank to be molded into the ridge in the vicinity of theoutward flanges are retained by the restraining portions.
 29. The methodfor producing a crash box according to claim 28, wherein the set plateincludes a locking section that is provided projecting from a surface ofthe plate and is butted against an inner surface of an end portion in alongitudinal direction of the tubular body.